The present invention relates to contact lenses, and more particularly to a multi-focal or bifocal contact lens made of two fused materials.
Multi-focal contact lenses are known in the art. Multi-focal contact lenses typically have concentric bands of different diopters. People then choose to see the image associated with the diopter suitable for the distance of the object. While some discomfort may be encountered when using single focal contact lenses, multi-focal lenses are known to cause discomfort more frequently. The reasons for the increase in difficulties are largely related to the discontinuities between the portions of the contact lens for near vision and the portions of the contact lens for far vision. These discontinuities can create irritations on the eye surface, or irritations on the eyelid, or trap impurities that may lead to infection, as well as optical distortions such as the presence of halos, etc. The optical distortions lead to eyestrain and fatigue.
Fused contact lenses are also known in the art and allow two materials having different indices of refraction to be used in the construction of the bands or zones. The fused construction may allow for smaller differences in curvature between bands and thus reduce discontinuities. However, the junction between fused materials may lead itself to a discontinuity or distortion in the shape of the lens under varying conditions.
It is an object of the present invention to provide a contact lens having a fused construction that has improved comfort, reduced optical distortions such as halos or the like, or reduced discontinuities, particularly in low light or night vision conditions.
It is an object of the invention to provide a contact lens having a fused construction with improved mechanical stability under varying conditions during use.
It is also an object of the invention to provide a method of manufacturing a fused multi-focal contact lens.
According to the invention, there is provided a fused multi-focal contact lens comprising a first portion having a first index of refraction and extending from a periphery of the lens over a concave side of the lens, and a second portion fused to the first portion and having a second index of refraction different from the first index of refraction. The lens comprises a central zone providing a first optic power and a first concentric band providing a second optic power. A central interface between the first portion and the second portion has a curvature substantially the same as a curvature of the concave side such that a thickness of the first portion within the central zone is substantially constant. The second portion forms a junction with the first portion on a convex side of the lens substantially outside of a field of view of a user""s eye. A transition profile between the junction and the central interface determines, along with the first and the second indices of refraction, the second optic power.
According to the invention, there is also provided a fused multi-focal contact lens comprising a first portion having a first index of refraction, a second portion fused to the first portion and having a second index of refraction different from the first index of refraction. The lens comprises a central zone providing a first optic power and a first concentric band providing a second optic power. A central interface between the first portion and the second portion within the central zone having a curvature substantially the same as a curvature of the concave side such that a thickness of one of the first and second portions is substantially constant, whereby the mechanical properties of the lens are more stable. The second portion forms a junction with the first portion substantially outside of a field of view of a user""s eye. A transition profile between the junction and the central interface determines, along with the first and the second indices of refraction, the second optic power.
According to the invention, there is also provided a fused multi-focal contact lens comprising a first portion having a first index of refraction, a second portion fused to the first portion and having a second index of refraction different from the first index of refraction. The lens comprises a central zone providing a first optic power and a first concentric band providing a second optic power. The lens comprises a central zone providing a first optic power and a first concentric band providing a second optic power. An interface between the first portion and the second portion extending substantially across all of the lens and having within the concentric band a curvature substantially the same as a curvature of the concave side such that a thickness of one of the first and second portions is substantially constant, whereby the mechanical properties of the lens are more stable. The interface having a change in curvature at a junction between the central zone and the concentric band wherein a profile of the interface within the central zone determines, along with the first and the second indices of refraction, the first optic power.